The Brain Learns Completely Differently Than We’ve Assumed Since The 20th Century


Source: Bar-Ilan University

Summary: Using new theoretical results and experiments on neuronal cultures, a group of scientists, has demonstrated that the central assumption for nearly 70 years that learning occurs only in the synapses is mistaken.


The brain is a complex network containing billions of neurons, where each of these neurons communicates simultaneously with thousands of other via their synapses (links). However, the neuron actually collects its many synaptic incoming signals through several extremely long ramified “arms” only, called dendritic trees. Previous work suggested that learning occurs in the brain by modifying the strength of the synapses, whereas neurons function as the computational elements in the brain. This has remained the common assumption until today. Using new theoretical results and experiments on neuronal cultures, a group of scientists from the Bar-Ilan University has demonstrated that the central assumption for nearly 70 years that learning occurs only in the synapses is mistaken. The study findings were published in the journal Nature.

Brain-Synapses-Dendrites

Image representing the old synaptic (red) and new dendritic (green) learning scenarios of the brain. In the center a neuron with two dendritic trees collects incoming signals via many thousands of tiny adjustable learning parameters, the synapses, represented by red valves. In the new dendritic learning scenario (right) only two adjustable red valves are located in close proximity to the computational element, the neuron. The scale is such that if a neuron collecting its incoming signals is represented by a person’s faraway fingers, the length of its hands would be as tall as a skyscraper (left). Credit: Prof. Ido Kanter

The newly suggested learning scenario indicates that learning occurs in a few dendrites that are in much closer proximity to the neuron, as opposed to the previous notion. Another important finding of the study is that weak synapses, previously assumed to be insignificant even though they comprise the majority of our brain, play an important role in the dynamics of our brain. They induce oscillations of the learning parameters rather than pushing them to unrealistic fixed extremes, as suggested in the current synaptic learning scenario. The new learning scenario occurs in different sites of the brain and therefore calls for a reevaluation of current treatments for disordered brain functionality. Hence, the popular phrase “neurons that fire together wire together“, summarizing Donald Hebb’s 70-year-old hypothesis, must now be rephrased.


More Information: Shira Sarda et al, “Adaptive nodes enrich nonlinear cooperative learning beyond traditional adaptation by links”, Nature (2018). https://www.nature.com/articles/s41598-018-23471-7 


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